As is well known, the laying of a pipeline in an underwater bed for conveying a gas or a liquid is carried out from a suitably equipped vessel. The pipeline portion comprised between said vessel and the submerged bed is always suspended and assumes in the space a curved geometrical configuration, the shape of which depends on a set of parameters such as diameter and thickness of the pipe, depth of the submerged bed, tractive force of the vessel, buoyancy of the same pipeline, etc. Now, it is very important to detect and to accurately determine during the laying operation the presence in the pipe of ovalizations and swellings so as to immediately stop the laying operation when these deformations exceed the prefixed tolerance limits, and the geometrical configuration of the pipeline, i.e. its curving, so as to avoid a squashing or breaking of the same pipeline by opportunely acting on the parameters putting the pipeline under tension when said curving tends to overcome the elastic strain limit for the said pipeline. On the other hand it should be kept in mind that the geometrical configuration of a pipeline is never contained in a plane, but in the space; said geometrical configuration is therefore wholly determined only when there are detected the projections of the same geometrical configuration on a vertical plane passing through the touching points between the pipeline and the vessel and the submerged bed respectively, and on a plane orthogonal to said vertical plane.
Some devices for use in detecting the geometrical configuration of a pipeline are already known by the prior art, but all these known devices, besides being expensive apparatus which work in a complicated and discontinuous way, interfere sometimes with the laying operations as they require the application and/or the recovery of transducers for detecting the geometrical configuration point by point, do not detect the geometrical configuration in the space, but only the projection of said geometrical configuration on a vertical plane, and furthermore do not detect the presence of incidental ovalizations or swellings.
An object of the present invention is to eliminate the above-said drawbacks and to provide a device allowing to steplessly detect in a simple and precise way both the deformations (ovalizations or swelling) of a submerged pipeline and the projections on two orthogonal planes of the geometrical configuration of said pipeline.
The device according to the invention comprises a selfpropelled carriage with four driving wheels, which is inserted and runs into a pipeline to be tested, said carriage being equipped with a system for feeling the inner surface of said pipeline so as to detect the geometrical shape of the pipe and hence whatever ovalizations or deformations which may be present, with a system sensitive to the slope of the carriage in a vertical plane and hence to the slope of the pipeline wherein the carriage runs, with a system sensitive to the shiftings in a horizontal plane of the carriage and hence of the pipeline wherein the carriage runs, and with a system for measuring the meters covered by the same carriage inside the pipeline.
According to an embodiment of the invention the said feeling system comprises a set of at least four feelers resiliently mounted, two by two opposed, on a head adjustable along the axis of the pipeline to be tested, each feeler being constituted by a lever backwardly inclined at a certain angle as to the running direction of the carriage, to the free end of each such lever there is pivotally mounted a small sliding and feeling wheel which is resiliently pressed against the inner surface of the pipeline, each said lever being connected by an inextensible wire to a first springloaded gear on which the said wire is wound and which meshes a second gear which is integral with the wiper of a potentiometer.
In such a way the shifting of any of the feelers owing to the presence of a swelling or deformation into the pipeline to be tested gives rise, through the inextensible wire, to a rotation of the said gears and hence of the wiper of the potentiometer so that a variable-resistance shifting transducer delivers an electric signal proportional to the value of said deformation.
According to a preferred embodiment of the invention the signals delivered by the transducers are sent via cable to the outside of the pipeline on the pipeline laying vessel where they are visualized or recorded by suitable instruments signaling in an acoustic way and/or by means of warning lights when the deformations exceed the prefixed tolerance limits so as to stop the running of the carriage.
According to another embodiment of the invention the said system sensitive to the slope in a vertical plane of the carriage and hence of the pipeline comprises a gravity inclinometer whose moving element is pivoted on a toothed pin meshing a small gear which is integral with the wiper of a potentiometer.
In such a way the variable-resistance transducer delivers a continuous voltage signal which is proportional to the second derivative of the line of the carriage and hence to the second derivative of the projection of the geometrical configuration of the pipeline on a vertical plane passing through the touching points between the pipeline and the submerged bed and the vessel respectively. According to another embodiment of the invention the said system sensitive to the shiftings in a horizontal plane of the carriage comprises a gyroscope acting in a known way on a variable-resistence transducer (potentiometer) so as to shift the moving wiper of the latter.
In such a way a continuous voltage signal is obtained which is proportional to the second derivative of the line representing the shiftings of the carriage in a projection of the geometrical configuration of the pipeline on a horizontal plane. Summing up, the said two continuous voltage signals allow the detection in a stepless way of the shape of the derivative of the geometrical configuration in the space of a pipeline and hence, practically, the shape of the same geometrical configuration.
According to another embodiment of the invention the said system for measuring the meters covered by the carriage inside the pipeline is constituted by a pulse tachometer comprising a contact switch which is mounted on one of the small sliding and feeling wheels of the feeling system and closes at every complete revolution of said wheel an electric circuit delivering a voltage pulse. According to a further embodiment of the invention the above-said voltage pulses delivered by the tachometer are added to the continuous signals delivered by the gravity inclinometer and by the gyroscope respectively and the two obtained addition signals are sent via cable on the vessel to the inlets of a two-pen recorder. In such a way in the recorder there are recorded two graphs illustrating the derivative of the projections of the geometrical configuration of the pipeline to be tested on a vertical plane and on a horizontal plane respectively, the meters covered by the carriage being marked on the same graphs; this allows the measuring of the value of the geometrical configuration at any point of the pipeline.
According to a preferred embodiment of the invention the carriage is equipped with an electromechanical or electronic counter for predetermining the number of meters of the pipeline in which there is an interest in detecting the geometrical configuration, so that the carriage is automatically stopped at the end of a detection, and with a timer for allowing the repetition at predetermined time intervals of the detection of the geometrical configuration by letting the carriage come back.
The invention will be now illustrated in the accompanying drawings which are merely exemplary and non-limiting embodiment, in that the adoption of constructional techniques or equivalent members different from those suggested herein lies within the scope of the present invention.